This invention relates broadly to abrading, sanding or polishing devices and more specifically to a lapping block for shaping and finishing the curved surface on a work piece. In particular, this invention relates to a lapping block for sanding and polishing the spherical surface of a projection screen used on modern and sophisticated aircraft simulators.
Various devices for finishing plane and in some instances, curved surfaces, be they concave or convex are known. In this connection, a simple block of wood with a piece of sand paper or emery cloth wrapped around has served as an apparatus for such finishing. For example, U.S. Pat. No. 752,475 issued to J. C. Smith on Feb. 16, 1904 disclosed an abrading tool for use with sand paper or emery cloth. This tool included a base with a handle as well as short bristles of brush tufts located between the block base and the sheet of emery cloth or paper. The tufts or short bristle provided a yielding or resilient backing which allowed an irregular or uneven surface to be readily smoothed by forcing the emery cloth into the hollows of the irregular surface. These tufts also yielded to any projection in the work piece and thereby permitted the emery cloth to slide over these projections. In this manner, the tufts help to achieve contact between the emery cloth and the work piece at all times.
According to another U.S. Pat. No. 2,214,515 issued to J. W. Vanderveer on Sept. 10, 1940, a block for abrading plane or curved surfaces is disclosed. According to this patent, a sanding block having an abrasive material attached to one face is constructed of narrow strips which are separated by a space or saw kerf except for a small portion. The space between the strips allows the face of the block having the abrasive material attached thereto to be readily formed into convex or concave surfaces. These surfaces are selectively curved along one axis such that they conform to the shape of the piece of work being finished. Narrow strips making up the block may also be completely separated to provide a method of easily adjusting the size of the sanding block.
Still another U.S. Pat. No. 2,434,581 issued to O. Ottoson on Jan. 13, 1948, discloses a holder for an abrasive material such as steel or brass wool. This patent discloses a base for holding the steel wool and includes a long handle so that a surface such as a floor can be scrubbed or cleaned while standing and without requiring contact of the hand and the steel wool.
U.S. Pat. No. 3,030,742 issued to W. T. Costello on Apr. 24, 1962, discloses a resilient pad suitable for use as a backing pad for hand sanding in an automobile body painting shop, etc. This flexible and resilient pad provides a means for achieving the superior finish of hand sanding while still providing a means for preventing the hands of the user from becoming raw and sore from constant contact with the sand paper. It will be appreciated, however, that this pad is only useful in final finishing and is not suitable if extensive abrading or removal of material is required.
From the above discussions, therefore, it will be appreciated that these various prior art sanding and abrading blocks suffer several disadvantages. As an example, these blocks are not suitable for extensive abrading of a complicated concave or convex surface without constant monitoring and manipulation to assure that the surface is being sanded uniformly. This is because, a flat abrading or sanding sheet or even a abrading or sanding sheet which curves in one plane cannot maintain total contact with the surface of a complex curved work piece. A second disadvantage, is that since sanding or abrading blocks require pressure to be exerted upon the block in order that the surface of the work piece can be quickly abraded, attempting to sand or lap a surface which is convex or concave can result in the curvature of the surface becoming distorted because of flat spots or other irregulatires due to unequal pressure.
It is therefore an object of this invention to provide an apparatus which allows the operator to sand or abrade a complex curved work piece without creating flat spots or other surface irregularities.
Another object of this invention is to provide a lapping block which will allow faster cutting or abrading of the surface while applying similar or less pressure to the sanding apparatus than is required in conventional sanding blocks.
A still further object is to provide an apparatus which will cause the sanding paper or emery cloth or abrading material to conform uniformly to the work surface.
A still further object is to provide a tool the employment of which on an uneven surface will allow the surface to be uniformly smoothed or rubbed.
Another object of this invention is to provide a tool which is inexpensive to manufacture and easy to use.
The goal of achieving greater realism in aircraft simulation and training units, has resulted in a need for complex and truly remarkable visual systems which are used with these training simulators. These visual systems must display to the trainee pilot a scene which substantially duplicates the scene the pilot would see in real life if he were flying the actual aircraft. To this end, the optics necessary for presenting the desired scene have become more and more complex. Consequently, wide angle displays using large curved mirrors and display screens have been developed. To achieve the desired realism and avoid distortions due to flaws and irregularities in the viewing surfaces, great care must be taken in manufacturing and finishing these viewing surfaces. In systems having small viewing surfaces, proper finishing is not overly difficult. However, certain of the new and sophisticated larger aircraft simulators having full view visual systems use spherical surfaces which must be precisely finished and polished. It will be appreciated, that none of the blocks used for hand abrading, lapping and polishing available heretofore were designed for the precision required for these complex and spherical viewing surfaces. It is therefore, another object of this invention to provide an apparatus which can be used in combination with sanding paper or emery cloth for abrading a spherical surface to a precise curvature.